(1) Field of the Invention
The present invention relates generally to industrial textiles and, more particularly, to a multilayer papermakers fabric for use on through-air dryer sections of paper making machines.
(2) Description of the Prior Art
Typically, through-air drying machines employ paper machine clothing having weave designs and properties for assisting the transportation and drying of the paper sheet through that section of the machine. A through-air dryer (TAD) is a honeycomb or generally porous large diameter suction roll that follows the press section of a paper machine. It is at least partially surrounded by a hood that blows hot air. The paper sheet is carried on the TAD fabric over the periphery of the TAD cylinder; hot air from the hood impinges onto the paper sheet, passes through the sheet and the TAD fabric supporting the sheet into the porous suction roll.
Prior art TAD fabrics commonly employ single layer fabric designs, although double layer fabrics have also been known to be used. By way of example, the following prior art references are considered relevant to this application:
U.S. Pat. Nos. 5,672,248, 5,746,887, and 6,017,417, issued Sep. 30, 1997, May 5, 1998, and Jan. 25, 2000, respectively, to Wendt, et al. for Method of making soft tissue products teaches tissue products with increased cross-machine direction stretch and method for producing same. This property is imparted to the tissue by making the tissue using a throughdrying fabric having from 5 to about 300 machine direction impression knuckles per square inch that are raised above the plane of the fabric. These impression knuckles are created by an extra warp system that is “embroidered” onto a base fabric structure.
U.S. Pat. No. 5,429,686, issued Jul. 4, 1995 to Chiu, et al. for Apparatus for making soft tissue products discloses a TAD fabric having a load bearing layer and a sculpture layer. The high impression warp knuckles of this layer are created by effectively embroidering a second warp system onto a base fabric load bearing layer similar to the above-referenced patents to Wendt, et at.
U.S. Pat. No. 6,237,644, issued May 29, 2001 to Hay et al. for Tissue forming fabrics teaches a single layer lattice-shaped fabric of a design to form an embossed fibrous web. The lattice design is formed by the pattern of weaving of the single layer fabric, and requires no additional filaments or elements to form the embossed design.
U.S. Pat. No. 4,239,065, issued Dec. 16, 1980 to Trokhan for Papermachine clothing having a surface comprising a bilaterally staggered array of wicker-basket-like cavities teaches a fabric for making soft, absorbent paper of relatively low density, and relatively isotropic stretch properties when creped. The fabric is woven such that a top-surface plane is formed by coplanar crossovers of filaments and sub-top-surface crossovers are distributed in a predetermined pattern throughout the clothing.
U.S. Pat. No. 6,110,324, issued Aug. 29, 2000 to Trokhan, et al. for Papermaking belt having reinforcing piles teaches a fabric having yarns disposed, in part, to the top surface plane to form knuckles, and further including reinforcing piles that resist applied loads and may prevent deflection of the knuckles during the papermaking process.
U.S. Pat. No. 6,000,440, issued Dec. 14, 1999 to Hay for Multi-layer papermaking fabric teaches a multi-layer fabric with paperside to lower surface weft ratios greater than 1 and all paperside weft yarns interlacing with the warp yarns in an identical manner. The paperside weft yarns intermittently buttress against adjacent paperside weft yarns and possess an average lateral crimp ratio of greater than 1.62, producing a fabric having reduced fabric openness and thus an air permeability of less than 275 c.f.m./ft2 (cubic feet per minute per square foot) or about 4450 m3/m2/h (cubic meters per square meter per hour) at ½ inch water pressure. The fabric has a reduced rate of dewatering for increasing sheet smoothness, reducing two sidedness, providing additional sheet support, and reducing void volume for minimal sheet rewetting.
However, disadvantageously, TAD fabrics of the prior art have typically not provided an optimal relationship between fabric properties such as air permeability and warp fill, and finished paper sheet properties, namely paper sheet bulk. Ideally, the paper sheet bulk is maximized without slowing the paper machine or otherwise negatively affecting the paper machine running parameters or other sheet properties.
Thus, there remains a need for an improved through-air dryer (TAD) fabric, which fabric is woven according to a selected weave pattern from a system of synthetic monofilament warp and weft yarns which is chosen to provide a warp fill in the fabric of at least 100%, sufficient air permeability for producing relatively high drying rates, and a surface topography which will contribute to increased paper sheet bulk without adversely affecting other paper machine running parameters, in particular, machine speed.